Abstract: The remediation of Cd contamination in farmland soil is of great significance to the safety of food production. Sedum plumbizincicola is a Cd hyperaccumulator discovered and reported in China. This study explored the characteristics of cadmium accumulation in S. plumbizincicola at different growth periods and its effects on available Cd content in rhizospheric soil. Moderately and lightly Cd contaminated farmland with the same parent material were selected for in-situ phytoremediation experiments, the aboveground biomass and Cd absorption of S. plumbizincicola were analyzed at early branching, branching peak, flowering peak and late flowering growth period, as well as the profiles distribution characteristics of soil pH and available Cd content in rhizospheric soil. The results show that: the biomass, Cd content and the amount of Cd accumulation in aboveground of S. plumbizincicola did not increase with the extension of planting time. The plant height of S. plumbizincicola in lightly Cd contaminated farmland was more than 60 cm at flowering peak period, and its fresh weight of one plant was up to 1.59 kg, and the amount of Cd accumulation in one plant was more than 2.26 mg. The highest Cd content in S. plumbizincicola was found in flowers, and the Cd contents of flowers in moderately and lightly Cd contaminated farmland were 1.60-3.42 times and 1.88-6.53 times of that in other parts, respectively at flowering peak period. There were significant differences in the amount of Cd accumulation in aboveground parts of S. plumbizincicola in moderately and lightly Cd contaminated farmland during the 4 growth periods, and the maximum Cd accumulation was at the peak of branching period and flowering period, respectively. The profile distribution characteristics of soil pH and available Cd content in rhizospheric soil firstly decreased and then increased with the increasing of soil depth and that near the root zone is slightly lower than far from the root zone. The soil pH in moderately Cd contaminated farmland was the lowest at the early branching period, and the soil pH of ＞2-6 cm near the root zone was 4.37-4.43, and the available Cd content was the lowest at the branching peak period, was 0.16-0.31 mg·kg^-1 near the root zone and its coefficient of variation was the lowest (26.5%). The decrease of soil pH is beneficial to the Cd absorption by S. plumbizincicola, and the biomass is the key factor affecting the phytoremediation efficiency of S. plumbizincicola.

Key words: Sedum plumbizincicola, rhizosphere, profile, growth period, phytoremediation efficiency